57,991 research outputs found
Uplink User Capacity in a CDMA System with Hotspot Microcells: Effects of Finite Transmit Power and Dispersion
This paper examines the uplink user capacity in a two-tier code division
multiple access (CDMA) system with hotspot microcells when user terminal power
is limited and the wireless channel is finitely-dispersive. A
finitely-dispersive channel causes variable fading of the signal power at the
output of the RAKE receiver. First, a two-cell system composed of one macrocell
and one embedded microcell is studied and analytical methods are developed to
estimate the user capacity as a function of a dimensionless parameter that
depends on the transmit power constraint and cell radius. Next, novel
analytical methods are developed to study the effect of variable fading, both
with and without transmit power constraints. Finally, the analytical methods
are extended to estimate uplink user capacity for multicell CDMA systems,
composed of multiple macrocells and multiple embedded microcells. In all cases,
the analysis-based estimates are compared with and confirmed by simulation
results.Comment: To appear in IEEE Transactions on Wireless Communication
A Quantum Multiparty Packing Lemma and the Relay Channel
Optimally encoding classical information in a quantum system is one of the
oldest and most fundamental challenges of quantum information theory. Holevo's
bound places a hard upper limit on such encodings, while the
Holevo-Schumacher-Westmoreland (HSW) theorem addresses the question of how many
classical messages can be "packed" into a given quantum system. In this
article, we use Sen's recent quantum joint typicality results to prove a
one-shot multiparty quantum packing lemma generalizing the HSW theorem. The
lemma is designed to be easily applicable in many network communication
scenarios. As an illustration, we use it to straightforwardly obtain quantum
generalizations of well-known classical coding schemes for the relay channel:
multihop, coherent multihop, decode-forward, and partial decode-forward. We
provide both finite blocklength and asymptotic results, the latter matching
existing classical formulas. Given the key role of the classical packing lemma
in network information theory, our packing lemma should help open the field to
direct quantum generalization.Comment: 20 page
Cores of Cooperative Games in Information Theory
Cores of cooperative games are ubiquitous in information theory, and arise
most frequently in the characterization of fundamental limits in various
scenarios involving multiple users. Examples include classical settings in
network information theory such as Slepian-Wolf source coding and multiple
access channels, classical settings in statistics such as robust hypothesis
testing, and new settings at the intersection of networking and statistics such
as distributed estimation problems for sensor networks. Cooperative game theory
allows one to understand aspects of all of these problems from a fresh and
unifying perspective that treats users as players in a game, sometimes leading
to new insights. At the heart of these analyses are fundamental dualities that
have been long studied in the context of cooperative games; for information
theoretic purposes, these are dualities between information inequalities on the
one hand and properties of rate, capacity or other resource allocation regions
on the other.Comment: 12 pages, published at
http://www.hindawi.com/GetArticle.aspx?doi=10.1155/2008/318704 in EURASIP
Journal on Wireless Communications and Networking, Special Issue on "Theory
and Applications in Multiuser/Multiterminal Communications", April 200
Random Access Channel Coding in the Finite Blocklength Regime
Consider a random access communication scenario over a channel whose
operation is defined for any number of possible transmitters. Inspired by the
model recently introduced by Polyanskiy for the Multiple Access Channel (MAC)
with a fixed, known number of transmitters, we assume that the channel is
invariant to permutations on its inputs, and that all active transmitters
employ identical encoders. Unlike Polyanskiy, we consider a scenario where
neither the transmitters nor the receiver know which transmitters are active.
We refer to this agnostic communication setup as the Random Access Channel, or
RAC. Scheduled feedback of a finite number of bits is used to synchronize the
transmitters. The decoder is tasked with determining from the channel output
the number of active transmitters () and their messages but not which
transmitter sent which message. The decoding procedure occurs at a time
depending on the decoder's estimate of the number of active transmitters,
, thereby achieving a rate that varies with the number of active
transmitters. Single-bit feedback at each time , enables all
transmitters to determine the end of one coding epoch and the start of the
next. The central result of this work demonstrates the achievability on a RAC
of performance that is first-order optimal for the MAC in operation during each
coding epoch. While prior multiple access schemes for a fixed number of
transmitters require simultaneous threshold rules, the proposed
scheme uses a single threshold rule and achieves the same dispersion.Comment: Presented at ISIT18', submitted to IEEE Transactions on Information
Theor
Multiaccess Channels with State Known to Some Encoders and Independent Messages
We consider a state-dependent multiaccess channel (MAC) with state
non-causally known to some encoders. We derive an inner bound for the capacity
region in the general discrete memoryless case and specialize to a binary
noiseless case. In the case of maximum entropy channel state, we obtain the
capacity region for binary noiseless MAC with one informed encoder by deriving
a non-trivial outer bound for this case. For a Gaussian state-dependent MAC
with one encoder being informed of the channel state, we present an inner bound
by applying a slightly generalized dirty paper coding (GDPC) at the informed
encoder that allows for partial state cancellation, and a trivial outer bound
by providing channel state to the decoder also. The uninformed encoders benefit
from the state cancellation in terms of achievable rates, however, appears that
GDPC cannot completely eliminate the effect of the channel state on the
achievable rate region, in contrast to the case of all encoders being informed.
In the case of infinite state variance, we analyze how the uninformed encoder
benefits from the informed encoder's actions using the inner bound and also
provide a non-trivial outer bound for this case which is better than the
trivial outer bound.Comment: Accepted to EURASIP Journal on Wireless Communication and Networking,
Feb. 200
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