10,899 research outputs found
Hybrid performance modelling of opportunistic networks
We demonstrate the modelling of opportunistic networks using the process
algebra stochastic HYPE. Network traffic is modelled as continuous flows,
contact between nodes in the network is modelled stochastically, and
instantaneous decisions are modelled as discrete events. Our model describes a
network of stationary video sensors with a mobile ferry which collects data
from the sensors and delivers it to the base station. We consider different
mobility models and different buffer sizes for the ferries. This case study
illustrates the flexibility and expressive power of stochastic HYPE. We also
discuss the software that enables us to describe stochastic HYPE models and
simulate them.Comment: In Proceedings QAPL 2012, arXiv:1207.055
Energy-Efficient Transmission Scheduling with Strict Underflow Constraints
We consider a single source transmitting data to one or more receivers/users
over a shared wireless channel. Due to random fading, the wireless channel
conditions vary with time and from user to user. Each user has a buffer to
store received packets before they are drained. At each time step, the source
determines how much power to use for transmission to each user. The source's
objective is to allocate power in a manner that minimizes an expected cost
measure, while satisfying strict buffer underflow constraints and a total power
constraint in each slot. The expected cost measure is composed of costs
associated with power consumption from transmission and packet holding costs.
The primary application motivating this problem is wireless media streaming.
For this application, the buffer underflow constraints prevent the user buffers
from emptying, so as to maintain playout quality. In the case of a single user
with linear power-rate curves, we show that a modified base-stock policy is
optimal under the finite horizon, infinite horizon discounted, and infinite
horizon average expected cost criteria. For a single user with piecewise-linear
convex power-rate curves, we show that a finite generalized base-stock policy
is optimal under all three expected cost criteria. We also present the
sequences of critical numbers that complete the characterization of the optimal
control laws in each of these cases when some additional technical conditions
are satisfied. We then analyze the structure of the optimal policy for the case
of two users. We conclude with a discussion of methods to identify
implementable near-optimal policies for the most general case of M users.Comment: 109 pages, 11 pdf figures, template.tex is main file. We have
significantly revised the paper from version 1. Additions include the case of
a single receiver with piecewise-linear convex power-rate curves, the case of
two receivers, and the infinite horizon average expected cost proble
Markov Decision Processes with Applications in Wireless Sensor Networks: A Survey
Wireless sensor networks (WSNs) consist of autonomous and resource-limited
devices. The devices cooperate to monitor one or more physical phenomena within
an area of interest. WSNs operate as stochastic systems because of randomness
in the monitored environments. For long service time and low maintenance cost,
WSNs require adaptive and robust methods to address data exchange, topology
formulation, resource and power optimization, sensing coverage and object
detection, and security challenges. In these problems, sensor nodes are to make
optimized decisions from a set of accessible strategies to achieve design
goals. This survey reviews numerous applications of the Markov decision process
(MDP) framework, a powerful decision-making tool to develop adaptive algorithms
and protocols for WSNs. Furthermore, various solution methods are discussed and
compared to serve as a guide for using MDPs in WSNs
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