4,657 research outputs found
Throughput-Delay Trade-off for Hierarchical Cooperation in Ad Hoc Wireless Networks
Hierarchical cooperation has recently been shown to achieve better throughput
scaling than classical multihop schemes under certain assumptions on the
channel model in static wireless networks. However, the end-to-end delay of
this scheme turns out to be significantly larger than those of multihop
schemes. A modification of the scheme is proposed here that achieves a
throughput-delay trade-off for T(n) between
and , where D(n) and T(n) are
respectively the average delay per bit and the aggregate throughput in a
network of n nodes. This trade-off complements the previous results of El Gamal
et al., which show that the throughput-delay trade-off for multihop schemes is
given by D(n)=T(n) where T(n) lies between and .
Meanwhile, the present paper considers the network multiple-access problem,
which may be of interest in its own right.Comment: 9 pages, 6 figures, to appear in IEEE Transactions on Information
Theory, submitted Dec 200
Information Theoretic Operating Regimes of Large Wireless Networks
In analyzing the point-to-point wireless channel, insights about two
qualitatively different operating regimes--bandwidth- and power-limited--have
proven indispensable in the design of good communication schemes. In this
paper, we propose a new scaling law formulation for wireless networks that
allows us to develop a theory that is analogous to the point-to-point case. We
identify fundamental operating regimes of wireless networks and derive
architectural guidelines for the design of optimal schemes.
Our analysis shows that in a given wireless network with arbitrary size,
area, power, bandwidth, etc., there are three parameters of importance: the
short-distance SNR, the long-distance SNR, and the power path loss exponent of
the environment. Depending on these parameters we identify four qualitatively
different regimes. One of these regimes is especially interesting since it is
fundamentally a consequence of the heterogeneous nature of links in a network
and does not occur in the point-to-point case; the network capacity is {\em
both} power and bandwidth limited. This regime has thus far remained hidden due
to the limitations of the existing formulation. Existing schemes, either
multihop transmission or hierarchical cooperation, fail to achieve capacity in
this regime; we propose a new hybrid scheme that achieves capacity.Comment: 12 pages, 5 figures, to appear in IEEE Transactions on Information
Theor
Linear Capacity Scaling in Wireless Networks: Beyond Physical Limits?
We investigate the role of cooperation in wireless networks subject to a
spatial degrees of freedom limitation. To address the worst case scenario, we
consider a free-space line-of-sight type environment with no scattering and no
fading. We identify three qualitatively different operating regimes that are
determined by how the area of the network A, normalized with respect to the
wavelength lambda, compares to the number of users n. In networks with
sqrt{A}/lambda < sqrt{n}, the limitation in spatial degrees of freedom does not
allow to achieve a capacity scaling better than sqrt{n} and this performance
can be readily achieved by multi-hopping. This result has been recently shown
by Franceschetti et al. However, for networks with sqrt{A}/lambda > sqrt{n},
the number of available degrees of freedom is min(n, sqrt{A}/lambda), larger
that what can be achieved by multi-hopping. We show that the optimal capacity
scaling in this regime is achieved by hierarchical cooperation. In particular,
in networks with sqrt{A}/lambda> n, hierarchical cooperation can achieve linear
scaling.Comment: 10 pages, 5 figures, in Proc. of IEEE Information Theory and
Applications Workshop, Feb. 201
Demystifying the Scaling Laws of Dense Wireless Networks: No Linear Scaling in Practice
We optimize the hierarchical cooperation protocol of Ozgur, Leveque and Tse,
which is supposed to yield almost linear scaling of the capacity of a dense
wireless network with the number of users . Exploiting recent results on the
optimality of "treating interference as noise" in Gaussian interference
channels, we are able to optimize the achievable average per-link rate and not
just its scaling law. Our optimized hierarchical cooperation protocol
significantly outperforms the originally proposed scheme. On the negative side,
we show that even for very large , the rate scaling is far from linear, and
the optimal number of stages is less than 4, instead of as required for almost linear scaling. Combining our results and the
fact that, beyond a certain user density, the network capacity is fundamentally
limited by Maxwell laws, as shown by Francheschetti, Migliore and Minero, we
argue that there is indeed no intermediate regime of linear scaling for dense
networks in practice.Comment: 5 pages, 6 figures, ISIT 2014. arXiv admin note: substantial text
overlap with arXiv:1402.181
Hierarchical Cooperation Achieves Optimal Capacity Scaling in Ad Hoc Networks
n source and destination pairs randomly located in an area want to
communicate with each other. Signals transmitted from one user to another at
distance r apart are subject to a power loss of r^{-alpha}, as well as a random
phase. We identify the scaling laws of the information theoretic capacity of
the network. In the case of dense networks, where the area is fixed and the
density of nodes increasing, we show that the total capacity of the network
scales linearly with n. This improves on the best known achievability result of
n^{2/3} of Aeron and Saligrama, 2006. In the case of extended networks, where
the density of nodes is fixed and the area increasing linearly with n, we show
that this capacity scales as n^{2-alpha/2} for 2<alpha<3 and sqrt{n} for
alpha>3. The best known earlier result (Xie and Kumar 2006) identified the
scaling law for alpha > 4. Thus, much better scaling than multihop can be
achieved in dense networks, as well as in extended networks with low
attenuation. The performance gain is achieved by intelligent node cooperation
and distributed MIMO communication. The key ingredient is a hierarchical and
digital architecture for nodal exchange of information for realizing the
cooperation.Comment: 56 pages, 16 figures, submitted to IEEE Transactions on Information
Theor
Opportunistic Relaying in Wireless Networks
Relay networks having source-to-destination pairs and half-duplex
relays, all operating in the same frequency band in the presence of block
fading, are analyzed. This setup has attracted significant attention and
several relaying protocols have been reported in the literature. However, most
of the proposed solutions require either centrally coordinated scheduling or
detailed channel state information (CSI) at the transmitter side. Here, an
opportunistic relaying scheme is proposed, which alleviates these limitations.
The scheme entails a two-hop communication protocol, in which sources
communicate with destinations only through half-duplex relays. The key idea is
to schedule at each hop only a subset of nodes that can benefit from
\emph{multiuser diversity}. To select the source and destination nodes for each
hop, it requires only CSI at receivers (relays for the first hop, and
destination nodes for the second hop) and an integer-value CSI feedback to the
transmitters. For the case when is large and is fixed, it is shown that
the proposed scheme achieves a system throughput of bits/s/Hz. In
contrast, the information-theoretic upper bound of bits/s/Hz
is achievable only with more demanding CSI assumptions and cooperation between
the relays. Furthermore, it is shown that, under the condition that the product
of block duration and system bandwidth scales faster than , the
achievable throughput of the proposed scheme scales as .
Notably, this is proven to be the optimal throughput scaling even if
centralized scheduling is allowed, thus proving the optimality of the proposed
scheme in the scaling law sense.Comment: 17 pages, 8 figures, To appear in IEEE Transactions on Information
Theor
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