153,878 research outputs found
On Joint Source-Channel Coding for Correlated Sources Over Multiple-Access Relay Channels
We study the transmission of correlated sources over discrete memoryless (DM)
multiple-access-relay channels (MARCs), in which both the relay and the
destination have access to side information arbitrarily correlated with the
sources. As the optimal transmission scheme is an open problem, in this work we
propose a new joint source-channel coding scheme based on a novel combination
of the correlation preserving mapping (CPM) technique with Slepian-Wolf (SW)
source coding, and obtain the corresponding sufficient conditions. The proposed
coding scheme is based on the decode-and-forward strategy, and utilizes CPM for
encoding information simultaneously to the relay and the destination, whereas
the cooperation information from the relay is encoded via SW source coding. It
is shown that there are cases in which the new scheme strictly outperforms the
schemes available in the literature. This is the first instance of a
source-channel code that uses CPM for encoding information to two different
nodes (relay and destination). In addition to sufficient conditions, we present
three different sets of single-letter necessary conditions for reliable
transmission of correlated sources over DM MARCs. The newly derived conditions
are shown to be at least as tight as the previously known necessary conditions.Comment: Accepted to TI
Asynchronous Joint Source-Channel Communication: An Information-Theoretic Perspective
Due to the increasing growth and demand for wireless communication services, new techniques and paradigms are required for the development of next generation systems and networks. As a first step to better differentiate between various options to develop future systems, one should consider fundamental theoretical problems and limitations in present systems and networks. Hence, some common ground between network information theory and mobile/wireless medium techniques should be explicitly addressed to better understand future generation trends.
Among practical limitations, a major challenge, which is inherent and due to the physics of many mobile/wireless setups, is the problem of asynchronism between different nodes and/or clients in a wireless network. Although analytically convenient, the assumption of full synchronization between the end terminals in a network is usually difficult to justify. Thus, finding fundamental limits for communication systems under different types of asynchronism is essential to tackle real world problems.
In this thesis, we study information theoretic limits that various multiuser wireless communication systems encounter under time or phase asynchronism between different nodes. In particular, we divide our research into two categories: phase asynchronous and time asynchronous systems.
In the first part of this thesis, we consider several multiuser networks with phase fading communication links, i.e., all of the channels introduce phase shifts to the transmitted signals. We assume that the phase shifts are unknown to the transmitters as a practical assumption which results in a phase asynchronism between transmitter sides and receiver sides. We refer to these communication systems as phase incoherent (PI) communication systems and study the problem of communicating arbitrarily correlated sources over them. Specifically, we are interested in solving the general problem of joint source-channel coding over PI networks. To this end, we first present a lemma which is very useful in deriving necessary conditions for reliable communication of the sources over PI channels. Then, for each channel and under specific gain conditions, we derive sufficient conditions based on separate source and channel coding and show that the necessary and sufficient conditions match. Therefore, we are able to present and prove several separation theorems for channels under study under specific gain conditions.
In the second part of this thesis, we consider time asynchronism in networks. In particular, we consider a multiple access channel with a relay as a general setup to model many wireless networks in which the transmitters are time asynchronous in the sense that they cannot operate at the same exact time. Based on the realistic assumption of a time offset between the transmitters, we again consider the problem of communicating arbitrarily correlated sources over such a time-asynchronous multiple access relay channel (TA-MARC). We first derive a general necessary condition for reliable communication. Then, by the use of separate source and channel coding and under specific gain conditions, we show that the derived sufficient conditions match with the general necessary condition for reliable communications. Consequently, we present a separation theorem for this class of networks under specific gain conditions. We then specialize our results to a two-user interference channel with time asynchronism between the encoders
Joint Source-Channel Coding over a Fading Multiple Access Channel with Partial Channel State Information
In this paper we address the problem of transmission of correlated sources
over a fast fading multiple access channel (MAC) with partial channel state
information available at both the encoders and the decoder. We provide
sufficient conditions for transmission with given distortions. Next these
conditions are specialized to a Gaussian MAC (GMAC). We provide the optimal
power allocation strategy and compare the strategy with various levels of
channel state information.
Keywords: Fading MAC, Power allocation, Partial channel state information,
Correlated sources.Comment: 7 Pages, 3 figures. To Appear in IEEE GLOBECOM, 200
Source-Channel Coding Theorems for the Multiple-Access Relay Channel
We study reliable transmission of arbitrarily correlated sources over
multiple-access relay channels (MARCs) and multiple-access broadcast relay
channels (MABRCs). In MARCs only the destination is interested in
reconstructing the sources, while in MABRCs both the relay and the destination
want to reconstruct them. In addition to arbitrary correlation among the source
signals at the users, both the relay and the destination have side information
correlated with the source signals. Our objective is to determine whether a
given pair of sources can be losslessly transmitted to the destination for a
given number of channel symbols per source sample, defined as the
source-channel rate. Sufficient conditions for reliable communication based on
operational separation, as well as necessary conditions on the achievable
source-channel rates are characterized. Since operational separation is
generally not optimal for MARCs and MABRCs, sufficient conditions for reliable
communication using joint source-channel coding schemes based on a combination
of the correlation preserving mapping technique with Slepian-Wolf source coding
are also derived. For correlated sources transmitted over fading Gaussian MARCs
and MABRCs, we present conditions under which separation (i.e., separate and
stand-alone source and channel codes) is optimal. This is the first time
optimality of separation is proved for MARCs and MABRCs.Comment: Accepted to IEEE Transaction on Information Theor
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