822 research outputs found
Random Access Transport Capacity
We develop a new metric for quantifying end-to-end throughput in multihop
wireless networks, which we term random access transport capacity, since the
interference model presumes uncoordinated transmissions. The metric quantifies
the average maximum rate of successful end-to-end transmissions, multiplied by
the communication distance, and normalized by the network area. We show that a
simple upper bound on this quantity is computable in closed-form in terms of
key network parameters when the number of retransmissions is not restricted and
the hops are assumed to be equally spaced on a line between the source and
destination. We also derive the optimum number of hops and optimal per hop
success probability and show that our result follows the well-known square root
scaling law while providing exact expressions for the preconstants as well.
Numerical results demonstrate that the upper bound is accurate for the purpose
of determining the optimal hop count and success (or outage) probability.Comment: Submitted to IEEE Trans. on Wireless Communications, Sept. 200
Scaling Laws of Cognitive Networks
We consider a cognitive network consisting of n random pairs of cognitive
transmitters and receivers communicating simultaneously in the presence of
multiple primary users. Of interest is how the maximum throughput achieved by
the cognitive users scales with n. Furthermore, how far these users must be
from a primary user to guarantee a given primary outage. Two scenarios are
considered for the network scaling law: (i) when each cognitive transmitter
uses constant power to communicate with a cognitive receiver at a bounded
distance away, and (ii) when each cognitive transmitter scales its power
according to the distance to a considered primary user, allowing the cognitive
transmitter-receiver distances to grow. Using single-hop transmission, suitable
for cognitive devices of opportunistic nature, we show that, in both scenarios,
with path loss larger than 2, the cognitive network throughput scales linearly
with the number of cognitive users. We then explore the radius of a primary
exclusive region void of cognitive transmitters. We obtain bounds on this
radius for a given primary outage constraint. These bounds can help in the
design of a primary network with exclusive regions, outside of which cognitive
users may transmit freely. Our results show that opportunistic secondary
spectrum access using single-hop transmission is promising.Comment: significantly revised and extended, 30 pages, 13 figures, submitted
to IEEE Journal of Special Topics in Signal Processin
Transmission Capacities for Overlaid Wireless Ad Hoc Networks with Outage Constraints
We study the transmission capacities of two coexisting wireless networks (a
primary network vs. a secondary network) that operate in the same geographic
region and share the same spectrum. We define transmission capacity as the
product among the density of transmissions, the transmission rate, and the
successful transmission probability (1 minus the outage probability). The
primary (PR) network has a higher priority to access the spectrum without
particular considerations for the secondary (SR) network, where the SR network
limits its interference to the PR network by carefully controlling the density
of its transmitters. Assuming that the nodes are distributed according to
Poisson point processes and the two networks use different transmission ranges,
we quantify the transmission capacities for both of these two networks and
discuss their tradeoff based on asymptotic analyses. Our results show that if
the PR network permits a small increase of its outage probability, the sum
transmission capacity of the two networks (i.e., the overall spectrum
efficiency per unit area) will be boosted significantly over that of a single
network.Comment: 6 pages, 5 figures, accepted by IEEE ICC 200
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